Trees shrouded in ghostly cocoons line the edges of a submerged farm field in the Pakistani village of Sindh, where 2010's massive floods drove millions of spiders and possibly other insects into the trees to spin their webs.

Beginning last July, unprecedented monsoons dropped nearly ten years' worth of rainfall on Pakistan in one week, swelling the country's rivers. The water was slow to recede, creating vast pools of stagnant water across the countryside. (See pictures of the Pakistan flood.)

"It was a very slow-motion kind of disaster," said Russell Watkins, a multimedia editor with the U.K.'s Department for International Development (DFID), the organization tasked with managing Britain's overseas aid programs.

According to Watkins, who photographed the trees during a trip to Pakistan last December, people in Sindh said they'd never seen this phenomenon before the flooding.

(See pictures: "World's Biggest, Strongest Spider Webs Found.")

As for what exactly had spun the webs, Watkins said: "There wasn't a scientific analysis of this being done. Anecdotally, I think it was pretty much any kind arachnid species, possibly combined with other insects.

"It was largely spiders," he added. "Certainly, when we were there working, if you stood under one of these trees, dozens of small, very, very tiny spiders would just be dropping down onto your head."

Editor's note: Corrected November 30, 2011, after it came to our attention that it's not certain that all the silk pictured was spun by spiders.

—Ker Than

Pictures: Trees Cocooned in Webs After Flood

Documented by an aid worker, millions of spiders and possibly insects took to trees to spin webs after floods inundated Pakistan in 2010.